Electrical coil



K. S. JOHNSON.

ELECTRICAL COIL.

APPLICATION FILED DEC: 22, I920.

1,424,72 Patented Aug. 1, 1922.

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flan/797% 5? J0/1/750/7 W L/QK/IZM UNITED STATES PATENT OFFICE.

KENNETH S. JOHNSON, OF JERSEY CITY, NEW JERSEY, ASSIGNOR T0 WESTERN ELEC- TBIC COMPANY, INCORPORATED, OF NEW YORK, N.

YORK.

Y., A CORPORATION OF NEW ELECTRICAL COIL.

Specification of Letters Patent.

Patented. Aug. 1, 1922.

T 0 all whom it may concern:

Be it known that I, KENNETH S. JOHN- SON, a citizen'of the United States, residing at Jersey City, in the county of Hudson, State of New Jersey, have invented certain new and useful Improvements in Electrical Coils, of which the following is a full, clear, concise, and exact description.

This invention relates to electrical coils, and in particular to that class of coils used in telephone substation circuits.

An object of this invention is to provide an electrical coil in which is combined effectively the usual transformer and the balancing network in an anti-side tone telephone circuit. Another object is to reduce the number of parts required in the subscribers set.

In general the invention consists in winding on the same magneticcore two closely coupled windings answering the purpose of the transformer, and a third winding somewhat loose-1y coupled to each of the transformer windings. This third winding performs a double function, acting as a trans former winding and as a balancing network.

It is well known that in order to properly balance any anti-side tone substation circuit so that there will be no side tone in the receiver of the transmitting station when transmitting, it is necessary for the impedance of that portion of the circuit which provides the balancing network to have effectively the same phase angle as that of the line to whichthe set is to be connected. In connection with common battery antiside tone sets, it has been found that the phase angle of the average line (at 800 to 1000 cycles) to which such sets are connected, is very close to zero, and consequently the balancing network in such circuits is essentially a non-inductive resistance. Examples of such circuits are shown in a general way in Patent No. 1,254,474 of January 22, 1918, to G. A. Campbell, and more specifically in my patent 1,396,760 of November 15, 1921.

Cases frequently arise, however, where the impedance of the line to which the set is connected has a highly positive phase angle, for example, where the impedance has considerable inductive reactance. This conditionfre uently occurs when one subscribers set is directly connected by an electrically short line to another subscribers set; Under these conditions since the balancing network of any anti-side tone set must have the same phase angle as that of the line, it is necessary to have the balancing network consist essentially of a resistance and an inductance, or what is effectively a retardation coil. The use of a retardation coil in addition to the transformer ordinarily required in anti-side tone substation circuits becomes relatively expensive and this invention provides one electrical coil which will fulfill the requirements of both.

In the drawing Fig. 1 represents-the coil shown part in section. Fig. 2 shows diagrammatically the windings on the coil.

Referring to Fig. 1, core 1 is composed of magnetic material, preferably silicon steel strips or iron wires, and covering said core is a suitable wrapper 2 of insulating material. Ends 6 and 7 of insulating material provided at the extremities of the core with wrapper 2, form a spool. Between ends 6 and 7 and supported on said spool is partition 8 of insulating material so located that the winding space between it and end 6 is symmetrical with respect to the ends oft-he core. Wound concentrically in said space are windings 3 and 4. Wound partly over windings 3 and 4 and partly in the space between partition 8 and end 7 is winding 5 which may, if desired, be two separate windings in series.

The windings 3 and 4 are closely coupled with respect to each other, and winding 5 is somewhat loosely coupled to these. By varying the amount of the winding 5 wound over 3 and 4, the degree of coupling may be varied to suit different circuit requirements. It will be seen that by winding 5 completely over 3 and 4, a very closely coupled relation will be obtained, and onthe other hand by winding 5 completely in the space between partition 8 and end 7, a somewhat loose coupling will result. -The latter relation gives a coefiicient of coupling of only approximately 50 percent between windings 3 and 5; and 4 and 5, the remaining inductance of winding 5 acting as a retardation coil in series with the coupled portion of the winding. The result of such a relation may be illustrated by the following practical example. Suppose windin 5 has a direct current resistance of 44 0 ins and self-inductance of .027 henry. The portion of this inductance which is coupled with the other winding,

balance the line impedance.

however, is only about .007 henry, leaving approximately .020 henry, acting as a retardation coil. In other words, this coil would be essentially identical to another coil in which winding 5 is wound entirely over windings 3 and 4:, but wound with such a number of turns as to give it a self-inductanoe of .007 henry plus a separate impedan ce coil inserted in series with the winding 5 (entirely over 3 and l), and having an inductance of .020 henry, the total resistance of the impedance coil and winding 5 (entirely over 3 and 4) being the same as that of winding 5 alone distributed as shown in Fi l.

n the case just described the phase angle of the balancing impedance (which at 796.4:

cycles was 44+J.020 5000:44+J 100: 109 /66. 2) was 66, which is somewhat higher than that usually needed to properly In applying this to electrically short lines such as in apartment house telephone systems, it has been found that the phase angle should be slightly less than 45. This is accomplished by winding 5 partly distributed over windings 3 and 4 as shown in Fig. l.

It will, therefore, be seen that any degree of coupling may be obtained between winding 5 and windings 3 and 4, or any desired phase angle may be given the net-work provided the phase angle is not greater than that which may be obtained by winding the entire balancing winding in the space be tween partition 8 and end 7.

What is claimed is:

1. An electrical coil comp-rising a magnetic core, a plurality of windings wound in concentric relation thereon, said core projecting equidistant from each end of said windings, a single windin wound on one projection of said core, said single winding loosel coupled to said concentric windings.

2. in electrical coil, a magnetic core, a plurality of concentric windings thereon, said core projecting beyond said windings, an additional winding distributed by winding part concentric with aforesaid concentric windings and part, adjacent thereto on said projecting core to give a predetermined coupling between said concentric windings and ing an electrical coil, said coil comprising a' transformer having a projecting core, an additional winding distributed over said transformer in such a manner as will give the same phase angle as that of said line.

In witness whereof, I hereunto subscribe my name this 17th day of December A. D.,

KENNETH S, JOHNSON. 

